34 intraepithelial lymphocytes (IELs) are located within the intestinal epithelial monolayer, either in contact with the epithelial basal surface along the basement membrane, or in the lateral intercellular space between epithelial cells and below the tight junction. 34 IELs have been shown to prevent or exacerbate intestinal disease depending on the context, but 34 IEL behavior and interactions with other cell types in the intestinal mucosa are largely undefined. Until now, 34 IELs were presumed to be sessile, yet my preliminary data demonstrate that 34 IELs exhibit dynamic migratory behavior resulting in extensive interactions with the epithelium. Furthermore, I have shown that 34 IEL motility is dependent upon epithelial and 34 IEL expression of the tight junction protein occludin, and that certain cytokines alter this dynamic migratory behavior both in vitro and in vivo. Together, these observations have led to the central hypothesis that disruption of mucosal homeostasis adversely affects occludin-dependent 34 IEL migration leading to the exacerbation of disease. The aims of this application are to 1) elucidate the molecular mechanisms by which 34 IELs and epithelial cells interact during 34 IEL migration, 2) determine the effect of 34 IEL migration in IL-15 mediated small intestinal disease and 3) determine how 34 IEL migration contributes to the protection or exacerbation of colitis. A combination of in vivo confocal microscopy, traditional mucosal immunology, and epithelial cell biology techniques will be used to provide new mechanistic insights into the contribution of 34 IEL migration and subsequent epithelial interactions during disease. Moreover, these studies will enhance our understanding of how 34 IELs function within the mucosal microenvironment to regulate health and disease development, and may ultimately lead to new therapeutic approaches designed to modulate 34 IEL motility as means to treat intestinal inflammation. These studies are the first step toward achievement of my long-term goal to identify epithelial/immune cell interactions and determine the relevance of these interactions to IBD and celiac disease. The proposed research and career development plan, along with my mentors, advisory committee and the interdisciplinary approaches encouraged at the University of Chicago, will provide the support and additional training necessary to become an independent investigator in an academic research environment.